inclusion criteria: * 1.adults aged 18 years and older. 2.previous completion of 2 or 3 doses of inactivated covid-19 vaccine and compliance with the vaccination procedures in the current instructions. the last dose of vaccination is 6 to 18 months (180 to 540 days, including the threshold) after the investigational vaccination, and proof of previous vaccination can be provided. 3.understand the content of the icf, and voluntarily sign the icf. 4.participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. 5.healthy participants or participants with mild underlying disease \[in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study\]. 6.female participants * surgically sterilized or ≥ 2 years post-menopause, or negative urine pregnancy test and willing to use effective contraception (e.g., condoms, iuds) within 90 days of investigational vaccination. contraceptive use is not allowed. * consent to not breastfeed during the study and for at least 90 days after investigational vaccination。 male participants subjects of childbearing potential who agree to use effective contraception (e.g., condoms, spermicide) within 90 days of study vaccination.

inclusion criteria: * 1.adults aged 18 years and older. 2.previous completion of 2 or 3 doses of inactivated covid-19 vaccine and compliance with the vaccination procedures in the current instructions. the last dose of vaccination is 6 to 18 months (180 to 540 days, including the threshold) after the investigational vaccination, and proof of previous vaccination can be provided. 3.understand the content of the icf, and voluntarily sign the icf. 4.participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. 5.healthy participants or participants with mild underlying disease \[in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study\]. 6.female participants * surgically sterilized or ≥ 2 years post-menopause, or negative urine pregnancy test and willing to use effective contraception (e.g., condoms, iuds) within 90 days of investigational vaccination. contraceptive use is not allowed. * consent to not breastfeed during the study and for at least 90 days after investigational vaccination。 male participants subjects of childbearing potential who agree to use effective contraception (e.g., condoms, spermicide) within 90 days of study vaccination.

inclusion criteria: 1.adults aged 18 years and older. 2.previous completion of 2 or 3 doses of inactivated covid-19 vaccine and compliance with the vaccination procedures in the current instructions. the last dose of vaccination is 6 to 18 months (180 to 540 days, including the threshold) after the investigational vaccination, and proof of previous vaccination can be provided. 3.understand the content of the icf, and voluntarily sign the icf. 4.participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. 5.healthy participants or participants with mild underlying disease [in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study]. 6.female participants surgically sterilized or ≥ 2 years post-menopause, or negative urine pregnancy test and willing to use effective contraception (e.g., condoms, iuds) within 90 days of investigational vaccination. contraceptive use is not allowed. consent to not breastfeed during the study and for at least 90 days after investigational vaccination。 male participants subjects of childbearing potential who agree to use effective contraception (e.g., condoms, spermicide) within 90 days of study vaccination.

inclusion criteria: 1.adults aged 18 years and older. 2.previous completion of 2 or 3 doses of inactivated covid-19 vaccine and compliance with the vaccination procedures in the current instructions. the last dose of vaccination is 6 to 18 months (180 to 540 days, including the threshold) after the investigational vaccination, and proof of previous vaccination can be provided. 3.understand the content of the icf, and voluntarily sign the icf. 4.participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. 5.healthy participants or participants with mild underlying disease [in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study]. 6.female participants surgically sterilized or ≥ 2 years post-menopause, or negative urine pregnancy test and willing to use effective contraception (e.g., condoms, iuds) within 90 days of investigational vaccination. contraceptive use is not allowed. consent to not breastfeed during the study and for at least 90 days after investigational vaccination。 male participants subjects of childbearing potential who agree to use effective contraception (e.g., condoms, spermicide) within 90 days of study vaccination.